/**
 * All rights reserved. Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jivesoftware.smackx.entitycaps;

import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.IOException;

/**
 * 
 * @author Florian Schmaus Based on code by Brian Wellington
 *         (bwelling@xbill.org)
 * 
 */
public class Base32Encoder implements StringEncoder {

	private static final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ2345678";

	@Override
	public String decode(String str) {
		ByteArrayOutputStream bs = new ByteArrayOutputStream();
		byte[] raw = str.getBytes();
		for (int i = 0; i < raw.length; i++) {
			char c = (char) raw[i];
			if (!Character.isWhitespace(c)) {
				c = Character.toUpperCase(c);
				bs.write((byte) c);
			}
		}

		while (bs.size() % 8 != 0)
			bs.write('8');

		byte[] in = bs.toByteArray();

		bs.reset();
		DataOutputStream ds = new DataOutputStream(bs);

		for (int i = 0; i < in.length / 8; i++) {
			short[] s = new short[8];
			int[] t = new int[5];

			int padlen = 8;
			for (int j = 0; j < 8; j++) {
				char c = (char) in[i * 8 + j];
				if (c == '8')
					break;
				s[j] = (short) ALPHABET.indexOf(in[i * 8 + j]);
				if (s[j] < 0)
					return null;
				padlen--;
			}
			int blocklen = paddingToLen(padlen);
			if (blocklen < 0)
				return null;

			// all 5 bits of 1st, high 3 (of 5) of 2nd
			t[0] = (s[0] << 3) | s[1] >> 2;
			// lower 2 of 2nd, all 5 of 3rd, high 1 of 4th
			t[1] = ((s[1] & 0x03) << 6) | (s[2] << 1) | (s[3] >> 4);
			// lower 4 of 4th, high 4 of 5th
			t[2] = ((s[3] & 0x0F) << 4) | ((s[4] >> 1) & 0x0F);
			// lower 1 of 5th, all 5 of 6th, high 2 of 7th
			t[3] = (s[4] << 7) | (s[5] << 2) | (s[6] >> 3);
			// lower 3 of 7th, all of 8th
			t[4] = ((s[6] & 0x07) << 5) | s[7];

			try {
				for (int j = 0; j < blocklen; j++)
					ds.writeByte((byte) (t[j] & 0xFF));
			} catch (IOException e) {
			}
		}

		return new String(bs.toByteArray());
	}

	@Override
	public String encode(String str) {
		byte[] b = str.getBytes();
		ByteArrayOutputStream os = new ByteArrayOutputStream();

		for (int i = 0; i < (b.length + 4) / 5; i++) {
			short s[] = new short[5];
			int t[] = new int[8];

			int blocklen = 5;
			for (int j = 0; j < 5; j++) {
				if ((i * 5 + j) < b.length)
					s[j] = (short) (b[i * 5 + j] & 0xFF);
				else {
					s[j] = 0;
					blocklen--;
				}
			}
			int padlen = lenToPadding(blocklen);

			// convert the 5 byte block into 8 characters (values 0-31).

			// upper 5 bits from first byte
			t[0] = (byte) ((s[0] >> 3) & 0x1F);
			// lower 3 bits from 1st byte, upper 2 bits from 2nd.
			t[1] = (byte) (((s[0] & 0x07) << 2) | ((s[1] >> 6) & 0x03));
			// bits 5-1 from 2nd.
			t[2] = (byte) ((s[1] >> 1) & 0x1F);
			// lower 1 bit from 2nd, upper 4 from 3rd
			t[3] = (byte) (((s[1] & 0x01) << 4) | ((s[2] >> 4) & 0x0F));
			// lower 4 from 3rd, upper 1 from 4th.
			t[4] = (byte) (((s[2] & 0x0F) << 1) | ((s[3] >> 7) & 0x01));
			// bits 6-2 from 4th
			t[5] = (byte) ((s[3] >> 2) & 0x1F);
			// lower 2 from 4th, upper 3 from 5th;
			t[6] = (byte) (((s[3] & 0x03) << 3) | ((s[4] >> 5) & 0x07));
			// lower 5 from 5th;
			t[7] = (byte) (s[4] & 0x1F);

			// write out the actual characters.
			for (int j = 0; j < t.length - padlen; j++) {
				char c = ALPHABET.charAt(t[j]);
				os.write(c);
			}
		}
		return new String(os.toByteArray());
	}

	private static int lenToPadding(int blocklen) {
		switch (blocklen) {
		case 1:
			return 6;
		case 2:
			return 4;
		case 3:
			return 3;
		case 4:
			return 1;
		case 5:
			return 0;
		default:
			return -1;
		}
	}

	private static int paddingToLen(int padlen) {
		switch (padlen) {
		case 6:
			return 1;
		case 4:
			return 2;
		case 3:
			return 3;
		case 1:
			return 4;
		case 0:
			return 5;
		default:
			return -1;
		}
	}

}
